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Dec 1, 2010
Four years after scientists in the US reported seeing "giant piezoresistance" in silicon nanowires, a team of researchers in France and Switzerland claims that this phenomenon may not exist after all.
Giant piezoresistance is a large change in electrical resistance that occurs when a material is stretched. After it was first reported in tiny silicon wires, claims were made that it could significantly improve nanoelectronic devices, such as nanoscale transistors, and help make ultrasensitive nanosensors.
Now, new work by Jason Milne and Alistair Rowe at the Ecole Polytechnique, Steve Arscott of IEMN-CNRS and Christoph Renner at the University of Geneva calls such applications into question.
Physicists have known about piezoresistance (PZR) – whereby the electrical resistance of a semiconductor changes when a small mechanical stress is applied to it – for many years. Giant piezoresistance occurs when there is a much larger change in resistance for the same applied strain. For example, the change in resistance per unit of strain (the "gauge factor") typically ranges up to 100 in bulk silicon but in giant PZR, this value can reach several thousand.
Giant PZR would find many practical applications. For example, it might be used to detect motion in nanomechanical systems (NEMS) because traditional detectors lose their sensitivity at these length scales. Furthermore, because mechanical stress is currently employed to enhance the performance of electronic devices (in so-called "strain engineering"), it might also help enhance nanoscale transistors too.
The very act of measuring the resistance changes its value Alistair Rowe, Ecole Polytechnique
Four years ago Peidong Yang's team at the University of California at Berkeley first observed giant PZR in silicon nanowires and the discovery created a flurry of interest in labs worldwide. Indeed, the researchers measured gauge factors up to almost 6000. The effect was thought to be a new phenomenon occurring in an otherwise well-characterized material resulting from the sample's reduced size and characteristic surface states.
In a paper just published in Physical Review Letters, the France-Switzerland team claims that these observations were probably artefacts in no way related to the mechanical stress applied to the silicon nanowires. They were, instead, caused by surface trapping of charges induced by the voltage applied to measure the resistance. "In other words, the very act of measuring the resistance changes its value," explained Rowe.
PZR is usually measured by performing a standard resistance measurement on a sample while gradually changing the applied mechanical stress on it. The trouble is that any non-stress-related drift in the value of the resistance cannot be separated from that caused by the applied stress.
The France-Switzerland team says it overcame this problem by applying an oscillating stress to its samples. In this way, stress repeatedly increases and then decreases as function of time. "This is a fairly standard technique (called heterodyne detection) in physics and engineering and is used to separate two or more signals and give artefact-free measurements," said Rowe.
According to Rowe, scientists had never applied heterodyne techniques to PZR measurements before, so previous measurements revealed large (but not stress-related) resistance changes in the silicon nanowires. "This meant that the resistance drift due to charge trapping (also known as dielectric relaxation) was assumed to be the result of the applied stress", he added. "This now appears to have been an incorrect assumption."
Yang himself disagrees: "They are reporting PZR measurements on a collection of top-down micro- and nano-wires while our measurements were on bottom-up grown nanowires. Their results might not actually be that surprising as we now all know that bottom-up synthetic bridging nanowires have quite different strain levels, surface states and dopant profiles from those of top-down fabricated ones. In fact, the lack of giant PZR effect in such nanowires was already reported back in 2003. However, the lack of giant PZR effect in these new fabricated samples should not automatically imply the same in our synthetic bridging nanowires.
The observed PZR effect in our nanowires, whether it is intrinsic or from the surface states effect, has already proven to be useful Peidong Yang University of California at Berkeley
"After all, the observed PZR effect in our nanowires, whether it is intrinsic or from the surface states effect, has already proven to be useful," he added. "For example, we recently demonstrated the first piezoresistively transduced very high frequency silicon nanowire resonators with on-chip electronic actuation at room temperature. We clearly showed that, for very thin silicon nanowires, their time-varying strain can be exploited for self-transducing the devices' resonant motions at frequencies as high as 100 MHz. This simply would not be possible without the enhanced PZR effect."
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Dec 1, 2010
A team of astronomers has made the first direct measurement of the atmosphere of an exoplanetary "super-Earth". The findings suggest that the exoplanet named GJ 1214b has either an atmosphere swarming with clouds or one enveloped in water vapour.
Since the discovery of the first extra-solar planet – or exoplanet – in 1995, over 500 more have subsequently been unveiled. While most of these are gas giants like Jupiter, astronomers are getting better at finding smaller exoplanets that could be more similar to Earth.
GJ 1214b weighs in at 6.5 Earth masses and is a so called super-Earth because it tips the scales at between twice and ten times the mass of our own planet. Discovered in 2009, and circling a star approximately 40 light-years from Earth, the exoplanet's low density implied that it is blanketed by an atmosphere. However, until this latest research, led by Jacob Bean at the Harvard-Smithsonian Center for Astrophysics, US, direct measurements of this atmosphere had remained elusive.
Bean and colleagues used a spectrograph, attached to the Very Large Telescope (VLT), to analyse light from the parent star as the planet passed in front of it. During such a transit some starlight passes through the planet's atmosphere and can be soaked up by its constituent chemicals. This produces a spectrum containing tell-tale fingerprints – gaps at wavelengths where light is absorbed by the atmosphere. Crucially, Bean's spectrum for GJ 1214b was featureless: there were no gaps in the data.
Such a result rules out models suggesting the possibility of a cloud-free, hydrogen-rich atmosphere similar in composition to Neptune. Hydrogen, the lightest element, doesn't cling very tightly to a planet, giving it a better chance of absorbing incoming sunlight. "A hydrogen-dominated atmosphere would be very 'puffy'," Bean told physicsworld.com. "It is this puffiness that would have given a very strong signature in the spectrum that we measured," he added.
The lack of such a signature leaves two rival explanations fighting to explain Bean's finding. "The featureless spectrum tells us that it is probably a very dense atmosphere. However, the alternative is that it does have a puffy atmosphere but with thick, high clouds that we can't see through, similar to Venus, or [Saturn's largest Moon] Titan," explained Bean.
I think we'll get the answer within a year, maybe even sooner Jacob Bean, Harvard-Smithsonian Center for Astrophysics
Should it turn out to be the former, the most likely chemical candidate is water vapour; GJ 1214b orbits so close to its host star that it could well be shrouded in steam. Bean is confident of nailing the answer soon: "I think we'll get the answer within a year, maybe even sooner, we just need longer wavelength observations. Whilst clouds and hazes give a uniform absorption over the wavelength range we used, over very large wavelengths you would expect a difference," he said.
However, some researchers are cautious. "They've done this looking through the Earth's atmosphere, which is never a friend to astronomy," Carole Haswell, an exoplanet researcher at the Open University, told physicsworld.com. "What they've done is very difficult; any slight systematic effects are going to have a huge effect on the conclusions that you draw. It's good, solid and exciting stuff but I'd like to see it checked from space, e.g. with Hubble," she added.
Should Bean's findings be confirmed, Haswell sees this area of research as a crucial part of finding a "second Earth". "If you can measure the composition of the atmospheres of planets like GJ 1214b then you are getting quite close to saying how similar they are to Earth. This is a big step in addressing the question of whether Earth is unique," she explained.
This is a pretty major stepping stone in getting to the end goal of finding an Earth-like planet with signatures of life David Sing, University of Exeter
David Sing, who researches exoplanet atmospheres at the University of Exeter, agrees. "There have been a number of spectral studies of so-called 'hot-Jupiters' but this is the first time it's been done for a terrestrial-type planet," he said. "This is a pretty major stepping stone in getting to the end goal of finding an Earth-like planet with signatures of life," he added.
And Haswell believes we've come along way in a short period of time, telling physicsworld.com: "The fact that in 1995 we didn't know of any planets around other stars and now we're measuring the atmospheres of planets in the same ball park as the Earth is amazing."
The findings are described in a paper published in Nature 468 669.
Colin Stuart is a science communicator, writer and broadcaster based in London
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Ever wondered how a fly effortlessly lands and runs on your window without falling off? Judging by the natural curiosity of most Physics World readers, it is probably the sort of thing you thought about when you first started exploring the world around you as a child. However, as you might have noticed back then if you tried to get a better look, it is really hard to see those little insect feet in action without any form of magnification.
As the childlike curiosity of scientists never ends, it is somehow no big surprise that this apparently simple question – of how a fly sticks to a surface instead of just sliding off – was addressed in the 17th century by some of the pioneers of optical microscopy, including Robert Hooke. Better optical lenses suddenly allowed researchers to explore the world beyond the resolution of their eyes for the very first time.
Even back then, scientists knew that there is more to insects than meets the eye. While the most basic system of mechanical interlocking found in arthropods is the claw, insects do not merely have a miniature version of this. Many surfaces in the natural world are simply not soft enough to allow claws to be inserted, or are too smooth to provide a safe grip. The question of how insects stick, crawl and run on vertical surfaces and even upside down remains as hotly debated between scientists now as it was in the 17th century.
One of the first books on microscopy was Experimental Philosophy, written by Henry Power in 1664. Along with detailed observations of various organisms, Power described and discussed the adhesive organs of the fly. He suggested that the fly's feet can hold the creature upside down using a "whitish viscous liquor" secreted via tiny sponges on its feet.
However, just one year later, Hooke (best known to physicists for his eponymous law of elasticity) sparked a heated debate by challenging Power's wet-adhesion theory. In his respected book Micrographia, Hooke speculated that on the length scale of a fly's foot, surfaces are rough enough that the feet can interlock and adhere using fine hairs (figure 1): "without the access or need of any such Sponges fill'd with an imaginary gluten, as many have, for want of good Glasses, perhaps, or a troublesome and diligent examination, suppos'd".
After this rather personal dispute, many researchers proposed and tested the mechanisms of insect adhesion over the subsequent 200 years. Even Jonathan Swift, the passionate Irish natural scientist, mentions how insects stick in his well-known 1726 novel Gulliver's Travels. Gulliver, exploring a land of giants during his second journey, is attacked by wasps one morning and complains that "these odious insects would sometimes alight upon my victuals, and leave their loathsome excrement, or spawn behind...which, our naturalists tell us, enables those creatures to walk with their feet upwards upon a ceiling".
By the mid-19th century, most scientists had written off insect adhesion as fully understood, as Power's theory of glue-based adhesion had been mostly accepted within the scientific community. Yet confusingly, in 1832 a different idea was introduced that, despite being proven wrong the following year, is still among the most popular "cocktail party" explanations. The idea came from German zoologist Herman Burmeister, who postulated that insects stick using "muscular suction cups". To check this theory, in 1833 the British naturalist John Blackwall placed insects in sealed cylinders, out of which he then pumped the air. He found that the insects' ability to adhere to the smooth inner surface was unaffected by the air pressure, and so dismissed Burmeister's theory. However, despite the evidence, many scientists continued to pursue the suction-cup idea, and only a few investigated fluid adhesion in the years that followed.
Meanwhile, in further studies Blackwall noticed that placing small quantities of water vapour, oil, wheat, pulverized chalk or gypsum onto clean glass surfaces prevented insects and spiders from sticking to them. "These facts, far from corroborating the mechanical theory," he concluded, "appeared quite inexplicable, except on the supposition that an adhesive secretion is emitted by the instruments employed in climbing."
After this flurry of activity in the early to mid-1800s, scientists soon turned their attention and their microscopes towards other wonders of nature's micro-cosmos, and insect adhesion became a largely forgotten quest – a backwater in the broader sweep of science.
Fast-forward to the present day, however, and the study of insects has come back into fashion. Elaborate instruments such as the scanning electron microscope and the atomic force microscope have allowed us to glimpse a new realm – the nano-cosmos. Scientists can now unmask even more of nature's mysteries, and engineers have realized that taking inspiration from the natural world can be a neat route to developing innovative products. For example, the adhesive organs of insects, spiders and geckos are better than many artificial adhesives, at least in terms of their versatility (see "Stewed and digested"), and the fact that they are reusable and work in dynamic situations.
During their lifetime insects need to attach and detach their feet many millions of times. Each of these steps risks damaging or contaminating the insect's feet, which would reduce their ability to stick. (Ever tried to reuse a Post-it note?) Insects get around this problem by using self-cleaning mechanisms, which rid the feet of any dirt to allow optimal stickiness, regardless of the number of steps taken. Such mechanisms have also been found in geckos.
While some insects remain stuck to a single surface for almost their entire lifetime, others run quickly carrying heavy loads or jump between surfaces. This requires their feet to be dynamic – to stick one moment and release the next. An outstanding example of this is the weaver ant Oecophylla smaragdina, whose feet can support a theoretical maximum of 100 times its body weight, according to Walter Federle and Thomas Endlein from the Insect Biomechanics Workgroup at Cambridge University in the UK (figure 2). However, the ant can still almost immediately detach its feet to place its next step.
Endlein has also shown that some insects can mechanically unfold their feet passively – without neuronal signals – in fractions of a second. This overrides any possible delay and is useful in unexpected events of mechanical disturbance, such as raindrops or a gust of wind. However, the details of how insects control their feet so quickly are still not fully understood. In particular, the adhesion control during jumping, which can be a change from firm adhesion to complete detachment within a fraction of a second, is the focus of ongoing research.
All insect feet have foot pads that can be classed as one of two functional designs: "hairy" or "smooth". In general, both types let the insect attach itself more strongly to a surface by conforming to substrates with roughness at different length scales. This explains why insects can stick to so many different surface types: from hard to soft; rough to smooth; on stone, glass, plastic and even Teflon.
Smooth adhesive pads can be found in many groups of insects – ants, bees, stick insects, grasshoppers, bugs and cockroaches. These insects possess a specialized organ, the arolium, which is located at the tip of the feet and consists of a very soft, cushion-like sac.
As already described by Hooke more than 300 years ago, the pads on the feet of flies, beetles and other insect groups are densely covered with flexible hairs arranged in arrays. Today, we know that similar structures can be found in many other creatures, such as geckos and spiders, indicating a general favourable design for adhesive structures. Although it is believed that hairy pads have several advantages over smooth ones, there is still an ongoing discussion in the biomechanics community about which is the better system (see, for example, J Bullock, P Drechsler and W Federle 2008 J. Exp. Biol. 211 3333).
Whether they are smooth or hairy, all insect feet have one thing in common: they use a nanometre-thin layer of fluid to help them stick to surfaces. Power already suggested that this is secreted using a "fuzzy kinde of substance like little sponges", which the fly can squeeze liquid out of "at pleasure". However, it was only recently that Federle and I were able to show that this 300-year-old idea is actually true for the smooth pads of insects. Using a motorized-stage to repeatedly (and carefully!) press the feet of insects onto smooth glass plates to simulate footsteps, we found that the amount of residue actually decreases with each step. Insects, in other words, have a limited volume of adhesive fluid in their feet. We also repeated the experiment using different walking speeds and it turns out that the sponges always refill at the same rate, no matter how fast the insects run. Nevertheless, it is still not known where the adhesive fluid is actually produced within the insect's body.
As for the nature of this fluid, it is often thought to be a kind of sticky glue. But if this were the case, how would insects that place their sticky feet down ever lift them up again? The wet-adhesive mechanism is thought to result from three physical principles of fluid mechanics: the forces of surface tension; the pressure difference between the fluid and the surrounding air (Laplace pressure); and the viscosity of the fluid. But as you may know from walking with wet feet beside a swimming pool, a layer of fluid can reduce adhesion and friction forces. So why, then, do insects use fluid-based adhesion at all, if the additional fluid layer bears the danger of reducing their ability to walk on smooth surfaces?
To answer this question, a more detailed knowledge of insect-feet forces is required. Federle, and Patrick Drechsler from the University of Würzburg in Germany, were among the first to actually measure the forces generated by placing single insect feet on well-defined substrates. Using a custom-made force transducer on a 3D motor stage, they gently pushed and pulled insects' feet along various smooth and rough surfaces. By comparing the forces generated on these substrates the researchers were able to show that an important function of the fluid appears to be filling in the gaps between the pad and the surface. This maximizes the contact area of the adhesive pad and increases adhesion to rough substrates.
Interestingly, Drechsler and Federle found that the sliding friction forces generated by insects' wet feet were substantially greater than expected. The experiments also revealed a significant static-friction component, which prevents a resting insect from sliding on smooth surfaces. Unfortunately, neither of these friction forces can be explained by assuming a continuous "simple" fluid layer between the feet and the substrates. Chemical analyses of footprint droplets also revealed nothing that might help to explain the high friction observed in fluid layers where one would expect slippage. The fluids appear simply to contain long-chained hydrocarbons, fatty acids, carbohydrates and amino acids.
It was only when the fluid was observed in situ, in the moment it is secreted into the contact zone, that its secret was revealed. In 2002 Federle and collaborators from the universities of Würzburg, Glasgow and Berkeley used interference reflection microscopy to discover that the adhesive fluid of ants and stick-insects is not a simple fluid but consists of two components that together form an emulsion. The experiments demonstrated that the bulk component of this emulsion is an oily substance, which is stable even over several days at room temperature. (This is probably what was discovered in insects' footprints about 300 years ago.) The second, smaller component is a highly volatile water-like substance that evaporates within fractions of a second when in contact with air, which explains why it had never been found in residues before. Federle and co-workers suggested that this two-phase structure might play an important role in the generation of friction forces.
To test this idea my colleagues and I again measured the forces generated by a single adhesive pad, but this time using a special polymeric surface. This smooth coating works like a selective sponge by only absorbing the short-lived watery phase of the emulsion and leaving the oily part behind. By making thick and thin polymer layers with different absorbing capacities, we were able to compare the forces generated with both fluids present with those with only the oily part present. Our results showed that the friction forces of smooth pads were significantly reduced without the watery phase present: the insects were slipping on their own oil. (We later put this finding to good use – see figure 3.)
It turns out that both phases are vital, and together they form a non-Newtonian Bingham fluid. This means that the fluid behaves like a solid when at rest, but with a viscosity that decreases when it is sheared. It is this property that provides resistance to sliding, complementing the simple capillary adhesion.
• Watch the cockroaches slide like firefighters down a pole with the patented "Insectislide" technology, in this video.
From what we know today, Henry Power was surprisingly accurate with his first observations about the adhesive mechanisms of insects in 1664. Two centuries later, in 1884, the German scientist Hermann Dewitz paid late tribute to Power's pioneering work by writing "Many different ideas [about insect adhesion] have been expressed so far; oddly enough, the correct one seems to be the oldest of them."
Insects have been sticking around for the last couple of million years and, although their adhesive organs have been studied for about the last 300 years, their tricks have still not lost any of their fascination. To the attentive observer, and imaginative research-grant applicant, even such a "simple" thing as a fly running across the office window still demonstrates a great selection from nature's box of tricks.
When an insect journeys thorough the world, it has to cope with a variety of different substrates with changing and unpredictable orientation, contamination, roughness and wettability. In fact, there are only a few known natural surface structures that insects cannot stick to – mostly carnivorous plants! One such plant is the carnivorous pitcher – so-named because it looks like a jug. Many varieties of the plant have a hydrophilic rim. When the rim is dry, ants are able to climb in to the pitcher to collect nectar from just under the rim's mouth and then climb back out again. But as Holger Bohn and Ulrike Bauer from the University of Cambridge showed during their PhD work in the last few years, air humidity or rain can easily form a very thin water layer on the plant's surface. This layer somehow foils the insect's usually reliable feet and makes them aquaplane into the bottom of the pitcher, where they are destined to stew in the plant's digestive juices. But surprisingly, some ants can walk on the plants when they are wet and do not slip at all. They can climb in and out of the pitcher with ease, and even swim within the digestive fluid.
• Watch some unlucky ants meet their fate, while others manage to avoid the deadly trap, in this video.
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Dec 1, 2010 The Quants: How a New Breed of Math Whizzes Conquered Wall Street and Nearly Destroyed It Scott Patterson 2010 Crown Business $27.00 hb 352pp
This past summer I spent the long US Independence Day weekend at a reunion with three of my undergraduate classmates. All of us went on to earn PhDs in physics, but I am the only practising physicist. The others work in finance – one at a hedge fund, the other two at major banks. They all seem to be enjoying their work, and they have obviously been very successful: our reunion took place near a famous ski resort, where one of the financiers has built a 1200 m2 retreat complete with gym, indoor pool and wine cellar.
Even the brightest graduate students in maths and physics know that their chances of assuming a position like that of their PhD supervisors are slim. For the last 20 years the cream of the crop of physicists leaving the field has gone on to positions in finance, typically in places such as New York or London. Once there, these individuals become hedge-fund managers, derivatives traders and risk managers, to take just a few examples from my own cohort.
So what do these people do? I have always been surprised that scientists in academia are not more curious about the lives of their former peers working in the "real world". For those who are interested, Scott Patterson's The Quants does an admirable job of exploring the increasingly mathematical and technological world of high finance, and the activities of the many physicists, mathematicians and engineers who inhabit it.
Patterson writes for the Wall Street Journal, and regular readers of the newspaper will recognize him as an insightful reporter who has covered a number of important topics over the years, most recently the rise of high-frequency trading. In researching the book, Patterson had access to a Who's Who of prominent "quants", a colourful group of characters with backgrounds and personalities that will be strangely familiar to anyone who has spent time among physicists. The term "quant" is short for "quantitative" and refers to those who apply mathematical or computational methods to finance.
Patterson begins by introducing the reader to ideas ranging from the basics of modern finance theory, such as efficient markets and random walks, to more esoteric topics such as the late Benoît Mandelbrot's use of Lévy distributions, or Gaussian copula and their role in the mortgage meltdown. It is worth noting that Patterson focuses primarily on proprietary trading and hedge funds, while spending much less time on the derivatives business or structured finance, two other areas where quants tend to be employed.
All this information makes an effective backdrop to the book's main story: the August 2007 quant-fund collapse that presaged the mortgage meltdown and subsequent global financial crisis. Patterson chronicles in detail how losses in the mortgage portfolios of banks and hedge funds forced them to sell off liquid assets such as the "vanilla" stocks (those of large Standard & Poors 500 companies) typically traded by large quant funds. This unanticipated deviation from the behaviour of financial models – in particular the wave of fear and paranoia that quickly spread among traders – led to huge losses for the quant funds. One prominent fund, Process-Driven Trading, lost $500m in a single month. This episode reminds us of the central role that human psychology – what the economist John Maynard Keynes called "animal spirits" – plays in markets, rendering them ultimately resistant to mathematical prediction.
To highlight the human element in this tale of financial collapse, Patterson includes many sketches of prominent quants. Among these, Ed Thorpe deserves Patterson's description as the godfather of quants. An academic mathematician who became famous in 1962 for his statistical analysis of the card game blackjack (recounted in his classic book on card counting Beat the Dealer), Thorpe later became one of the earliest and most successful hedge-fund managers. The similarities between games such as blackjack or poker and modern finance are significant: strategies in each can be refined through mathematical analysis, but success is ultimately still dependent on luck and the ability to manage risk.
Perhaps the most successful of all quants is Jim Simons. In the early 1970s Simons was a graduate student of the mathematician Shiing-Shen Chern at the University of California, Berkeley. I doubt he was a physics student, as Patterson states, although Chern–Simons theory does play an important role in theoretical physics. In 1978 Simons left academia in favour of finance. Today, the Renaissance Technologies hedge funds he set up employ mainly former scientists, including mathematicians, physicists and statisticians, and its Medallion Fund boasts consistently positive returns that are unequalled by any other fund. Simons attributes this to his employees' training in science, having once told the Wall Street Journal that "the advantage scientists bring into the game is less their mathematical or computational skills than their ability to think scientifically. They are less likely to accept an apparent winning strategy that might be a mere statistical fluke."
Among the younger quants profiled, Peter Muller seems the most interesting. An idealist who was frequently conflicted about his career in finance, Muller built the Process Driven Trading (PDT) group at Morgan Stanley, which at one point in the late 1990s accounted for a quarter of all profits for the entire firm. During this period, he would sometimes jet off to the Hawaiian island of Kauai for some hiking, leaving his lieutenants and algorithms to manage PDT's multi-billion-dollar financial positions. Like many of his fellow quants, Muller is an avid poker player, but he is also a musician who occasionally performs in the New York City subway and has released two CDs.
The broader financial crisis that followed the quant-fund collapse is not the major focus of this book. Readers seeking a deep discussion of its causes and consequences should look elsewhere. From my own investigations, I would say that while quants played an important role in the crisis, their influence was secondary to other causes, such as a housing bubble, misaligned incentives within banks and imprudence on the part of government-sponsored entities such as Fannie Mae and Freddie Mac, which provided funding for countless high-risk mortgages.
But that does not absolve quants entirely. It is a pity that although Patterson gives us a broad survey of quant finance, he devotes little space to the bigger question: are developments such as the mathematization of markets and the flow of top brains to financial activities good for society? On this matter, perhaps it is best to leave the last word to Charlie Munger, the long-time investment partner of financial guru-in-chief Warren Buffet. Writing in 2006, Munger had the following to say about the "brain drain" of top talent into finance.
"I regard the amount of brainpower going into money management as a national scandal. We have armies of people with advanced degrees in physics and math in various hedge funds and private-equity funds trying to outsmart the market. A lot of…older people…can remember when none of these people existed…At Samsung, their engineers meet at 11 p.m. Our meetings of engineers [meaning our smartest citizens] are also at 11 p.m., but they're working on pricing derivatives. I think it's crazy to have incentives that drive your most intelligent people into a very sophisticated gaming system."
Steve Hsu is professor of theoretical physics at the University of Oregon, a founder of two Silicon Valley software start-ups and author of the blog Information Processing
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Dec 1, 2010 Physicist-turned-composer Edward Cowie has long believed there are deep connections between mathematics and music. Michael Banks finds out what inspired him to produce a homage to the great Ernest Rutherford
Hanging on the bare-brick walls in the small, dimly lit basement of St George's concert hall in Bristol, UK, is a series of 24 artists' prints by the composer Edward Cowie. They appear in the aptly named Crypt Gallery, where visitors gather before shows, and were drawn especially to accompany each piano piece of Cowie's latest work Rutherford's Lights – a set of 24 "studies in light and colour for piano". But as well as bringing together art and music, Cowie's latest work seeks to marry together physical theories of light with music. Indeed, the inspiration for each of the 24 piano pieces came from the classic physics textbook The Theory of Light by Thomas Preston, which was first published in 1912.
Wave Motion (the 1st movement)Edward Cowie talks about the first movement of Rutherford's Lights. Music performed by Richard Casey.
Cowie is no stranger to physics, having studied the subject at Imperial College London. Speaking to Physics World in the Crypt Gallery, Cowie shoots from the hip when talking about the many attempts to fuse physics and music. He says he likes to recite one of his favourite poems called "The Unholy Marriage", written by the English poet David Holbrook, which describes a fateful crash when a motorcyclist takes his girlfriend for a ride around town. Holbrook, rather morbidly, describes the pair as having been "married" together by the high-speed collision.
"I would say that a lot of partnerships between art and science are the David Holbrook version," says Cowie, 67. "If you put a scientist and a composer in a food mixer, would you say they have collaborated?". One example of such an "unholy marriage", in his view, was Constant Speed performed by Rambert Dance Company, which was inspired by Einstein's scientific achievements and was commissioned by IOP Publishing (which produces Physics World) in 2005. "It was a fantastic thing to do and was very inventive," says Cowie. "But if they ever claimed one was about the other, then they were wrong – the ballet was not about Einstein; the ballet was about ballet and the music was about entertainment."
Cowie is hopeful that Rutherford's Lights, released on CD last month by UHR and for which IOP Publishing paid him a composer's fee, will not be seen as a David Holbrook version of an art–science collaboration – but rather as a musical piece that takes inspiration, as he puts it, from the "language of science". "I wouldn't say that physics influences my music," says Cowie. "But I could not have written the work without my training in physics."
Rutherford's Lights has recently been on tour around the UK, including being performed at St George's and culminating in a performance at the National Portrait Gallery late last month. The work, however, began its journey on the other side of the world, when Cowie was in Australia as director and founder of the Australian Arts Fusion Centre at James Cook University, Townsville. While in Queensland, Cowie was browsing in a bookshop when he was surprised to stumble across a copy of The Theory of Light. But he was in for an even bigger shock when he opened the book to find a message written in 1904 and signed by the nuclear physicist Ernest Rutherford himself to one of his students. Cowie promptly snapped it up – and for only $4.
Preston's book, which remains one of Cowie's most treasured possessions, is central to Rutherford's Lights, and is integral in each of the 24 pieces. "It is a homage to Rutherford," Cowie says. Each piece in Rutherford's Lights is, however, based on a specific chapter from Preston's book. The work is meant to be a journey through the book, beginning with simple descriptions of transverse waves at the beginning to more complicated theories of light later on. "There was an incredible division between the chapters in the book that I could see they were each separate pieces," says Cowie. "What I liked about Preston's book is that it is not dry. How he has constructed the language to describe physical properties is beautiful, almost musical."
Compounding of Simple Vibrations (the 3rd movement)Cowie speaks about how the piano can illustrate "complex expressions of the theories of light".
The first piece in Rutherford's Lights is called "Wave Motion". Sitting in St George's, Cowie pulls out a musical score of the piece in which the opening parts looks like a wave propagating along the page. "It is not difficult to talk about propagation and think acoustically," says Cowie, who calls Rutherford's Lights a "major breakthrough" in his music. Indeed, he says he would just sit at the piano with a chapter of Preston's book open and just attempt to put the equations and meaning of Preston's words into music. He would study the formulas and attempt to give their musical equivalence. "I am trying to make a piece of music whose quantity and quality is connected to light and its propagation," he says.
Edward Cowie was born in Birmingham, UK, in 1943. By the age of seven, he had started teaching himself music and the piano. But it was the influence of his parents, who wanted him to do a "proper vocation", that meant he went to Imperial to study physics. Cowie was still learning the piano and violin in his spare time, as well as doing the odd performance, which earned him money to pay for his education. "I didn't really see a difference between physics and music," says Cowie. "Everything has a numerical basis: music is about numbers just as much as maths is." But Cowie's love of music was still his driving force, and while at Imperial he also went to the Slade School of Fine Art at University College London to study painting as an external student.
After doing a Bachelors in music, in 1973 Cowie completed a PhD at Leeds University, which included studying music, physics and genetics. He was also awarded a Doctorate of Music by Southampton University in 1976. In the music world, Cowie obtained early recognition with the 1975 BBC Proms commission Leviathan for large orchestra, followed by popular works including the Piano Concerto (1976), the opera Commedia (1976) as well as Concerto for Orchestra (1982).
Various academic appointments in Germany and the US followed, eventually leading Cowie to take up a position as head of the School of Creative Arts at the University of Wollongong in Australia in 1983 and, six years later, as director of the Australian Arts Fusion Centre at James Cook University, Townsville. After losing funding for the centre, he finally returned to the UK in 1996 as director of research at Dartington College of Arts in Devon.
Following his retirement in 2008, Cowie is now hoping to foster more collaborations between science and the arts, beginning with Rutherford's Lights. "The divisive language between arts and sciences are artificial," says Cowie. "What we need is a bridge dialogue between them." Cowie is currently in discussion with the Oxford University particle physicist Brian Foster about making a set of violin pieces that will trace a "timeline" for the subject of particle physics.
Like many composers working in the early 1970s, Cowie came under the influence of the music of the "Second Viennese School". This included a method of musical composition invented by the Austrian-born composer Arnold Schoenberg. It employs a row of 12 different notes in the chromatic scale – a musical range with 12 equally spaced pitches, each a semitone apart – that can be permutated and combined to enable a kind of "lattice and grid approach" to the placement of musical pitches. Schoenberg's pupil, the composer Anton Webern, extended the idea further by applying combinatorial mathematics.
Natural Lights (the 18th movement)Cowie outlines how he applies the mathematics of light to natural phenomena such as rapidly moving water.
In adopting these techniques, and with his understanding of mathematics, Cowie was able to write complex music. However, he felt that his music at that time was too "system based" and he abandoned the technique in the mid-1970s. However, the use of mathematics in music fostered the notion that they are inextricably linked. "Physics is about patterns, written through equations – the language of mathematics" says Cowie. "Music is also about patterns, so you can relate and link them."
To demonstrate the links between music and mathematics, Cowie recalls the time in 2003 when he was commissioned by the BBC to produce a "sound portrait" of the Cambridge University physicist Stephen Hawking for the 125th anniversary of the National Portrait Gallery. Cowie travelled to Cambridge to meet Hawking to discuss the piece, who he knew liked music. After talking about music and physics for more than four hours, Hawking concluded that contemporary music had lost its way – it had no structure, he complained – and that he had no time for it. Cowie naturally did not agree. "If music has lost its way, then hasn't mathematics as well?" he asked. After a pause from Hawking, he slowly typed "Touché".
Born: Birmingham, 1943 Education: BSc physics, Imperial College, London (1961–1964); Bachelor of music, Southampton (1970); PhD in music, Leeds University (1971–1974); Doctorate in Music, Southampton University (1976) Career: Professor of composition, University of Lancaster (1973–1983); head of the School of Creative Arts at the University of Wollongong, Australia (1983–1988); director of the Australian Arts Fusion Centre at James Cook University, Townsville (1989–1994); director of research at Dartington College of Arts in Devon (1996–2008) Family: Married, two daughters Hobbies: Reading, sailing, bird-watching
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Dec 1, 2010 Robert P Crease witnesses one of the last inspections of the official SI kilogram standard
Once a year, a century-old ritual unfolds at the International Bureau of Weights and Measures (BIPM) outside Paris. It takes place in the basement of the BIPM's main lab building, which houses a vault secured with three locks. Three antique keys, held by citizens of different countries, open these locks. At the annual meeting of the BIPM's governing board – the International Committee for Weights and Measures (CIPM) – the three key holders produce the keys, open the vault, unlock a safe inside the vault and inspect its principal contents: the platinum–iridium cylinder that defines the kilogram.
This year's ritual, on 13 October, was unusual. It was not just that BIPM director Andrew Wallard (UK) and CIPM president Ernst Göbel (Germany) are retiring, making this their last year as key holders. Nor was it that the third key holder, Claire Béchu of the French Archives, was an hour late, delayed by a strike that snarled French traffic for most of the week. The atmosphere was different because a major change is afoot: the cylinder may soon be removed and dethroned.
The BIPM was created by the Treaty of the Metre in 1875, a landmark in the history of measurement, globalization and international co-operation. The ritual began a few years later when the BIPM's two international prototypes – of the metre and kilogram – were moved to the safe. In 1960 the metre was redefined in terms of the wavelength of light, thus dethroning the metre bar as the standard. (The metre was redefined again in 1983 in terms of the speed of light.) For most of the rest of the 20th century, metrologists could not even foresee the possibility of similarly replacing the kilogram with a natural standard.
However, advancing technologies now make this not only possible but inevitable. One agenda item at this year's CIPM meeting, the 99th, was to draft a resolution to be submitted next year to the organization to which the CIPM reports – the General Conference on Weights and Measures (CGPM) – that sets out a plan to redefine the kilogram and three other SI base units. If adopted, all SI units will eventually be defined in terms of natural constants.
In short, the platinum–iridium cylinder may not keep its status in the vault much longer, as it will cease to define the kilogram. Within the next few years, Wallard expects to move it from the safe to a laboratory for measurements in the transition to a new definition.
The 18 CIPM members engaged in last-minute debate on how to phrase the redefinition. Some wanted the language to be aimed at the general public, others preferred technical language for professional metrologists, while still others thought the definition ought to be technical but with accompanying explanations.
In the end, the group agreed on a "statement of intention" to redefine using fundamental constants, but only to proceed when the mise en pratique – in other words, the way in which the definition is to be technologically implemented – is available, agreed and producing consistent results. Furthermore, the group agreed to spread awareness of the potential redefinition and its consequences. Part of this effort will take place at an upcoming meeting of the Royal Society in London next month.
The looming redefinition meant that more than the usual number of spectators lined up to see the kilogram standard; not only CIPM members but BIPM staff and a few invited outsiders, including me. One could not help but be awestruck. For 121 years this cylinder has ruled over an international network of masses and scales that stretches from laboratories in national and local metrology offices into everyday life in the form of grocery stores, post offices and home scales. The cylinder is both a thing and an institution. And its days are numbered.
"It's so small!" exclaimed many of those who squeezed down the narrow staircase into the tiny room containing the safe. The cylinder is, in fact, a mere 39 mm high and as much in circumference. Another surprise for many of the spectators – including me – was that although the cylinder is protected by three bell-jars, it is not in a vacuum. The prototype turns out to be most stable in air, and might outgas in a vacuum. Spectators excitedly held up cameras and mobile phones to take pictures, the way they do at the Mona Lisa, housed at the Louvre across the Seine. Unlike the Mona Lisa, the international kilogram prototype is unharmed by flash photography – though by my extrapolation, Leonardo da Vinci's iconic work suffers more photography in 15 min than the prototype does in a century.
The CIPM's draft resolution must still be debated by the CGPM at its 24th meeting in October next year. But two technologies appear on the verge of satisfying criteria for implementation, and the CGPM is expected to take steps towards a revision. "It's a significant step," says Wallard. "It would provide, for the first time, an anchoring of all the base units of SI to fundamental constants, from which we can build up the whole system."
The visitors began to walk back upstairs and headed to the traditional champagne reception in the BIPM's fabulously beautiful gardens overlooking Paris, with the Eiffel Tower in the distance. Wallard, Göbel and Béchu recorded the temperature and relative humidity, and signed a document attesting that they had verified the presence of the international kilogram prototype and its official copies. They secured the safe, and shut and locked the door of the vault with their three keys, securing the cylinder for what may be its last sovereignty as the ruler of the international network of weights, although it will still have a key role to play in implementing a future redefinition.
The kilogram seemed unperturbed.
• A full feature article on the redefinition of the kilogram will appear in the March 2011 issue of Physics World
Robert P Crease is chairman of the Department of Philosophy, Stony Brook University, and historian at the Brookhaven National Laboratory, US
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Nov 30, 2010
Academics in Iran have been left in a state of critical fear following the murder in Tehran yesterday of nuclear physicist Majid Shahriari and the attempted assassination of another nuclear researcher, Fereydoon Abbasi.
The separate attacks occurred yesterday morning and both were carried out by unidentified assailants on motorbikes who attached explosives to the victims' vehicles as they travelled through the capital. Both scientists were based in the faculty of nuclear engineering at the Shahid Beheshti University in Tehran and they are both said to be key figures in Iran's controversial nuclear programme.
Iranian president, Mahmoud Ahmadinejad, immediately blamed the attacks on foreign enemies saying that "undoubtedly the hand of the Zionist regime and Western governments is involved". As yet, however, no nation or group has claimed responsibility.
"Everyone is shocked. Programmed assassination of scientists is the last thing we could imagine," says Reza Mansouri, a cosmologist at Sharif University in Tehran and a former Iranian deputy science minister. He confirmed that the widely held view in Iran is that this attack was carried out by foreign agents.
Shahriari was a nuclear researcher and his publication record suggests that he specialized in medical applications of nuclear physics, with a particular interest in modelling neutron transport processes. His role in Iran's nuclear programme was confirmed by Akbar Salehi, head of Iran's atomic energy agency, who says that Shahriari was involved in "one of the great projects" of the agency. "Majid Shahriari was one of my students for years and had a good cooperation with the organization," Salehi told the Islamic Republic News Agency.
Fereydoon Abbasi, the scientist who survived, appears to have a larger involvement with Iran's nuclear programme. In 2007 his name was added to the United Nations Security Council's sanctions list for his involvement in "nuclear or ballistic missile activities".
Monday's attacks follow the assassination in January of another Iranian physicist, Masoud Alimohammadi, a quantum mechanics and field theory specialist at Tehran University, who was killed by a remote-controlled bomb attached to the side of a motorcycle. The similarities between the attacks have left Iranian academics in an acute state of fear.
Despite the government's conviction that the murders have been carried out by Israeli or US special services, there is also speculation that the attackers could have belonged to one of a number of organizations within the Middle East. The speculation is fuelled by the continuing secrecy that surrounds Iran's nuclear programme and the increasingly complicated political situation in the Middle East.
Similarly, the motive for assassinating these particular men is not clear, particularly given their seemingly disparate research interests. One thing they do share is that all three men held roles in SESAME – Synchrotron-light for Experimental Science and Applications in the Middle East – a project that aims to create the region's first major international research centre by building a synchrotron light source in Jordon. Shahriari is listed as having been an adviser to the project, while Abbasi is a member of the Iranian advisory committee to SESAME, and Alimohammadi was a member of the council.
SESAME president Chris Llewellyn Smith, who is also a former director-general of CERN, says that he does not remember Shahriari though the official records state that he did attend one council meeting. Llewellyn Smith does, however, recall meeting Alimohammadi but he, likewise, was only able to attend one meeting before he was killed.
Llewellyn Smith is keen to point out that synchrotrons such as SESAME are not in any sense nuclear facilities. "They are accelerators that are designed to produce intense light with wavelengths ranging from the infrared to X-rays, which are used to study matter on scales ranging from biological cells to atoms," he says.
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Wave Motion (the 1st movement)Edward Cowie talks about the first movement of Rutherford's Lights. Music performed by Richard Casey.
Compounding of Simple Vibrations (the 3rd movement)Cowie speaks about how the piano can illustrate "complex expressions of the theories of light".
Natural Lights (the 18th movement)Cowie outlines how he applies the mathematics of light to natural phenomena such as rapidly moving water.